The correlation between chemically induced immune defects and biochemical defects in lymphoid tissues (thymus, spleen, bone marrow) and specific-populations of lymphoid cells (pleuripotent stem cells, granulocyte-macrophage precursors, T-cells, B-cells, macrophages) are being investigated. Rate limiting enzymes in monophosphate shunt, glycolysis and tricarboxylic acid, marker enzymes in macrophages, and enzymes of heme metabolism are being assayed. Change in substrate flow through these biosynthetic pathways were caused by immunotoxic chemicals and correlated with specific functional defects in the immune system.